Select E2 enzymes differentially regulate parkin activation and mitophagy

Loss-of-function mutations in the genes encoding PINK1 and Parkin are the most common causes of recessive Parkinson's disease (PD). Both together mediate the selective degradation of mitochondrial proteins and whole organelles via the proteasome and the autophagy/lysosome pathway (mitophagy). The mitochondrial kinase PINK1 activates and recruits the E3 ubiquitin (Ub) ligase Parkin to de-energized mitochondria. However, Parkin's cognate E2 co-enzymes in this Ub-dependent pathway have not been investigated. Here, we discovered in total four E2s that either positively or negatively regulate Parkin's activation, translocation and enzymatic functions during mitochondrial quality control. UBE2D family members and UBE2L3 redundantly charge the RING/HECT hybrid ligase Parkin with Ub, resulting in its initial activation and translocation to mitochondria. UBE2N however primarily operates through a different mechanism to mediate the proper clustering of mitochondria a prerequisite for degradation. Strikingly, in contrast to UBE2D, UBE2L3 and UBE2N, depletion of UBE2R1 results in enhanced Parkin translocation and clustering upon mitochondrial uncoupling. Our study uncovered redundant, cooperative or antagonistic functions of distinct E2 enzymes in the regulation of Parkin and mitophagy may suggest a putative role in PD pathogenesis.